Single Skeletal Muscle Fiber Elastic and Contractile Characteristics in Young and Older Men

The current investigation was designed to: (a) assess the impact of aging on elastic characteristics of single skeletal muscle fibers from young (N 6) and older men (N 6); and (b) correlate the potential changes, with the fiber contractile properties. Chemically skinned single muscle fibers (n 235) from vastus lateralis muscle were maximally activated. Maximal force and cross-sectional area were measured, and specific force calculated. The slack test was used to measure maximal unloaded shortening velocity. A quick release of 0.15 % of fiber length was applied to determine instantaneous stiffness. The myosin heavy chain isoform composition of each single fiber was determined by sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS– PAGE). Aging induces changes in both fiber elasticity (i.e., increased instantaneous stiffness) and contractility (i.e., reduced specific force and unloaded shortening velocity) in type I and IIa fibers. However, the changes in fiber stiffness may not directly influence contractile char-acteristics alterations. SARCOPENIA is a term referring to a loss of skeletalmuscle mass and strength in older humans [for review, see (1)]. Physiological studies of single muscle fibers have shown impairments in the contractile properties that ma